Rotary cylinder device

ABSTRACT

A plurality of guide shafts which are disposed parallel to an input/output shaft (a first input/output shaft, a second input/output shaft) are assembled in a case body which holds a cylinder in which first and second piston sets, move reciprocally. A first guide bearing, which abuts both side surfaces of a first piston body and receives only lateral pressure generated by the reciprocal movement, and a second guide bearing, which abuts both side surfaces of a second piston body and receives only lateral pressure generated by the reciprocal movement, are assembled coaxially and separated in an axial direction on each guide shaft.

TECHNICAL FIELD

The present disclosure relates to a rotary cylinder device, which is capable of mutually converting rotation of an input/output shaft and reciprocal movement of pistons in cylinders, more precisely relates to various types of driving devices, e.g., compressor, vacuum pump, fluid rotary device, internal-combustion engine.

BACKGROUND ART

A fluid machinery, in which pistons are provided in cylinders arranged in a radial direction with respect to a crank shaft and which is capable of sucking and pressure-feeding a fluid by pumping pressure generated by converting rotation of the crank shaft into reciprocal movement of the pistons, has been known (see Patent Literature 1: Japanese Laid-open Patent Publication No. S56-141079).

In the fluid machinery, damaging seal cups of piston heads and uneven abrasion of sliding surfaces of the cylinders will be caused by sliding resistance between the piston heads and the sliding surfaces, and energy loss of a driving source and electric consumption will be increased by frictional loss, thus another rotary cylinder device, which is capable of solving the above described disadvantages by relatively rotatably assembling piston sets to an eccentric cam capable of relatively rotating about a crank shaft so as to reduce a counter force applied to piston heads from sliding surfaces of cylinders and capable of reducing frictional loss and energy consumption, has been developed (see Patent Literature 2: Japanese Laid-open Patent Publication No. 2011-19080).

The rotary cylinder unit disclosed in Patent Literature 2 is now being actually used for, for example, a fluid pump of oxygen-condensing equipment for home medical cure. The oxygen-condensing equipment increases oxygen concentration of air to 90% or more and supplies the condensed oxygen to a patient through a nose cannula so as to cure, for example, chronic bronchitis. The rotary cylinder device repeats compressing air, feeding the compressed air and sucking air by converting rotation of a driving shaft into reciprocal movement of a piston.

CITATION LIST Patent Literature

-   -   Patent Literature 1: Japanese Laid-open Patent Publication No.         S56-141079     -   Patent Literature 2: Japanese Laid-open Patent Publication No.         2011-19080

SUMMARY OF INVENTION Technical Problem

In the rotary cylinder device disclosed in Patent Literature 2, linear reciprocal movement of piston sets, which are perpendicularly assembled to the eccentric cam, is guided by guide bearings, which are provided to both sides of piston bodies in moving directions, or guide bearings, which are provided in guide holes of the piston bodies formed in a lengthwise direction, so that sliding resistance between the piston heads and the cylinders can be reduced.

However, the above device is sufficient for the equipment installed at home or in a hospital; but, in case of using the guide bearings, eight guide bearings are provided on the both sides of the piston bodies in the moving directions (see FIG. 4 of Patent Literature 2) so many guide bearings are required; on the other hand, in case of using the guide bearings provided in the guide holes formed in the piston bodies in the lengthwise direction (see FIG. 10 of Patent Literature 2), a diameter of the piston bodies must be increased, therefore installation areas of the both cases must be large and the equipment cannot be downsized, so the above described device is not sufficient for a transportable oxygen-condensing equipment capable of improving QOL (Quality of Life) of a patient. To downsize the equipment with maintaining conventional pump performance, small-diameter piston sets must be linearly reciprocally moved by rotating a small-size motor, which is a driving source, at a high speed, but the guide bearings cannot be assembled in small spaces.

Further, each of the guide bearings are held like a cantilever, so durability of guide shafts is lowered by the reciprocal movement of the piston bodies.

Solution to Problem

Disclosures of the following embodiments are thought for solving the above described problems, so an object is to provide a rotary cylinder device in which piston bodies of a piston unit is shortened in the lengthwise direction to reduce the installation area and number of guide bearings is reduced to the required minimum so as to decrease number of parts, thereby promoting a reduction in size and improving the durability of the device.

The disclosures of the following embodiments at least have the following structures.

In the rotary cylinder device, rotation of an input/output shaft rotatably supported by a case body is converted into reciprocal movement of a plurality of piston sets perpendicularly arranged with respect to an eccentric cam according to the principle of hypocycloid, a plurality of guide shafts, which are disposed parallel to the input/output shaft, are assembled in the case body, which accommodates a piston unit having first and second piston sets assembled to the eccentric cam and positioned in an axial direction, and a first guide bearing, which abuts both side surfaces of a first piston body and receives only lateral pressure generated by the reciprocal movement, and a second guide bearing, which abuts both side surfaces of a second piston body and receives only lateral pressure generated by the reciprocal movement, are assembled coaxially and separated in the axial direction on each of the guide shafts.

As described above, a plurality of the guide shafts disposed parallel to the input/output shaft are assembled in the case body in the state where the first guide bearing, which abuts both side surfaces of the first piston body and receives only lateral pressure generated by the reciprocal movement, and the second guide bearing, which abuts both side surfaces of the second piston body and receives only lateral pressure generated by the reciprocal movement, are assembled coaxially and separated in the axial direction, so that an installation area of the case body accommodating the piston unit can be highly reduced.

Therefore, each of the piston bodies can be shortened in the lengthwise direction so that the device can be downsized, and the guide bearings may be provided at an intersection part of the first piston body and the second piston body, so providing four guide bearings is enough thereby number of parts can be reduced and downsizing the device can be promoted

Preferably, each of the guide shafts has a projected part, which is radially outwardly projected, a shaft part thereof including the projected part is fitted into a shaft hole formed in the case body, and rotation of the shaft part is prohibited.

With this structure, the rotation stopper is constituted by fitting the shaft part including the projected part into the shaft hole, so that abrasion between the guide shafts and the case body can be prevented, vibration of the guide shafts can be also prevented and durability can be improved.

Preferably, both shaft ends of each of the guide shafts are held by corner parts where the first piston body and the second piston body are intersected in the case body, and each of the guide shafts is assembled to a position at which the first guide bearing abuts both side parts of the first piston body and the second guide bearing abuts both side parts of the second piston body.

With this structure, it is sufficient to provide required minimum number of the guide shafts and the guide bearings to the corner parts where the first piston body and the second piston body are intersected, so the device can be downsized. Further, the both end parts of each of the guide shafts are held by the case body, so that vibration of the guide shafts can be restrained, and durability of the device can be improved due to low vibration and low noise.

Advantageous Effects of Invention

In the above described rotary cylinder device, each of the piston bodies assembled to the piston unit can be shortened in the lengthwise direction so as to reduce the installation area, and number of guide bearings can be reduced to the required minimum so as to decrease number of parts, thereby promoting a reduction in size and improving the durability of the device can be realized. Further, even if high speed rotary operation is performed, friction loss can be reduced, so that the small size rotary cylinder device capable of improving energy saving can be realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a rotary cylinder device.

FIG. 2 is an axial sectional view of the rotary cylinder device.

FIG. 3 includes a plan view of the rotary cylinder device in which a first case member is omitted, and a plan view thereof in which a second case member is omitted.

FIG. 4 is an exploded perspective view of the first case member, a piston unit and the second case member of the rotary cylinder device.

FIG. 5 is a perspective view of the rotary cylinder device in which the first case member and the second case member are omitted.

FIG. 6 is a perspective view of the rotary cylinder device shown in FIG. 4 in which the first case member is omitted, and cylinders are detached from the second case member.

FIG. 7 is a perspective view of the piston unit in which the second case member of FIG. 6 is omitted.

FIG. 8 is a perspective view of the piston unit from which seal cups and seal cup holders are detached.

FIG. 9 is a partial perspective view showing arrangement of a second piston body and a second bearing.

FIG. 10 is a partial perspective view showing arrangement of a first piston body and a first bearing.

FIG. 11 is a partial exploded perspective view of the rotary cylinder device.

FIG. 12 includes explanation views showing relationship between a rotation orbit of a first crank shaft around an input/output shaft, a rotation orbit of a second crank shaft around the first crank shaft and linear reciprocal movement of a piston set.

FIG. 13 includes explanation views for comparing an installation area of the rotary cylinder device of the embodiment with that of the conventional device.

FIG. 14 is graphs showing relationships between the motor rotation speed of the rotary cylinder device and output thereof.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will now be described with reference to the attached drawings. Firstly, a rotary cylinder used in a fluid pump will be explained, as an example, with reference to FIGS. 1-13. In the rotary cylinder device, linear reciprocal movement of pistons in cylinders and rotation of an input/output shaft are mutually converted, and the converted motion can be inputted or outputted.

In FIG. 1, an input/output shaft is rotatably held by a case body 3, which is constituted by a first case member 1 and a second case member 2. The input/output shaft is constituted by a first input/output shaft 4 a and a second input/output shaft 4 b (see FIG. 4). The first case member 1 and the second case member 2 are integrated by screwing fixing-screws 3 a (see FIG. 11) with screw holes, as described later. The second input/output shaft 4 b has an end surface, in which a concave part 4 c is formed (see FIG. 2) and, the shaft can be connected to a motor shaft, not shown, so that direct drive can be performed. Ends of the first input/output shaft 4 a and the second input/output shaft 4 b are respectively exposed from through-holes formed in end surfaces of the first case member 1 and the second case member 2 and held.

Cylinders 5 are arranged to face four side surfaces of the case body 3. In the present embodiment, they are respectively sandwiched between the first case member 1 and the second case member 2, so that they are held in the side surfaces of the case body 3. Opening parts of the cylinders 5 provided in the four side surfaces of the case body 3 are closed by cylinder heads 6 and head covers 7. Each of the cylinder heads 6 is fixed to the side surface of the case body 3 (the first case member 1 and the second case member 2), together with the head cover 7, by fixing screws 7 a (see FIG. 2).

As shown in FIG. 2, a first end surface cover 1 a is fixed to an end surface (an upper surface in FIG. 1) of the first case member 1, through a sealing member 8, by fixing screws 1 b. A second end surface cover 2 a is fixed to an end surface (a lower surface in FIG. 1) of the second case member 2, through a sealing member 8, by fixing screws 2 b. An attachment plate 9 is fixed on the end surface of the first case member 1 by fixing screws 10 (see FIG. 11).

As shown in FIG. 2, the first input/output shaft 4 a is rotatably supported, through a second bearing 2 c, in the second case member 2. The second input/output shaft 4 b is rotatably supported, through a first bearing 1 c, in the first case member 1. The first input/output shaft 4 a is integrated with a first balance weight 11 a. The second input/output shaft 4 b is integrated with a second balance weight 11 b. The first and second balance weights 11 a and 11 b are provided to produce mass balances (static balances) of rotatable members around the input/output shaft (the first input/output shaft 4 a and the second input/output shaft 4 b) including a first crank shaft 12 and a piston unit P described later.

In FIG. 2, the first crank shaft 12 is eccentrically arranged with respect to an axis of the input/output shaft. Concretely, one end (a lower end in FIG. 2) of the first crank shaft 12 is fitted into the first balance weight 11 a and fixed by a fixing screw 12 b in a state where a pin 12 a is inserted. Similarly, the other end (an upper end in FIG. 2) of the first crank shaft 12 is fitted into the second balance weight 11 b and fixed by a fixing screw 12 d in a state where a pin 12 c is inserted.

As shown in FIG. 2, a cylindrical eccentric cam 13 is capable of relatively rotating about the first crank shaft 12, and a first piston set 14 and a second piston set 15 (hereinafter referred to as “piston unit P”) are capable of relatively rotating with respect to the eccentric cam 13. Note that, in each of the piston sets, seal cups and sealing members including piston rings and sealing members are integrated with piston head of a piston. They will be concretely explained.

The eccentric cam 13 has a center through-hole 13 a, which is formed into a hollow cylindrical shape, and has second crank shafts 16 a and 16 b (see FIG. 12), which are eccentrically arranged with respect to the axis of the first crank shaft 12. In the present embodiment, the first piston set 14 and the second piston set 15 are perpendicularly arranged with respect to each other, so the second crank shafts 16 a and 16 b are arranged around the first crank shaft 12 with a phase difference of 180°. The eccentric cam 13 is made of, for example, stainless steel and integral-molded by a manner of MIM (Metal Injection Mold).

In the piston unit P, a connecting part, which connects the axis of the input/output shaft and the axis of the first crank shaft 12 (i.e., the first balance weight 11 a and the second balance weight 11 b) to each other, acts as a first crank arm. Further, a connecting part, which connects the axis of the first crank shaft 12 and the axes of the second crank shafts 16 a and 16 b to each other, acts as a second crank arm (see FIG. 12).

In FIG. 2, the eccentric cam 13 has the cylindrical hole 13 a, through which the first crank shaft 12 acting as a rotation center is penetrated, and cylindrical bodies 13 b, which are eccentrically arranged with respect to the cylindrical hole, is extended from both sides of the eccentric cam in the axial direction. Axes of the cylindrical bodies 13 b coincide with the second crank shafts 16 a and 16 b (see FIG. 12). Bearing holders 17 a and 17 b are press-fitted into the cylindrical hole 13 a from both sides or adhered on a hole surface thereof. The bearing holders 17 a and 17 b are assembled in a state where they abut axial end surfaces of the eccentric cam 13. Bearing holding parts 17 c and 17 d, which are capable of respectively holding second bearings 18 a and 18 b whose diameter is greater than at least that of the cylindrical hole 13 a, are formed in the bearing holders 17 a and 17 b. With this structure, the bearings having high load resistance performance can be assembled, so that durability of the second bearings 18 a and 18 b can be improved.

The second bearings 18 a and 18 b, which are assembled to the bearing holding parts 17 c and 17 d of the bearing holders 17 a and 17 b, support the eccentric cam 13 in a state where the eccentric cam can be relatively rotated with respect to the first crank shaft 12. The first crank shaft 12 becomes a center of relative rotation of the eccentric cam 13.

Third bearings 19 a and 19 b are respectively assembled to outer circumferences of the pair of cylindrical bodies 13 b, which are eccentrically arranged with respect to the axis of the cylindrical hole 13 a and axially extended from the both side. The first and second piston sets 14 and 15, which are intersected with each other, are assembled to the eccentric cam 13, with third bearings 19 a and 19 b, in a state where the piston sets can be relatively rotated with respect to the eccentric cam.

Principle of rotation of the first crank shaft 12 and the second crank shafts 16 a and 16 b around the input/output shaft (the first input/output shaft 4 a and the second 4 b) and linear reciprocal movement (hypocycloid movement) of the piston sets will be explained with reference to FIGS. 12A-12D. In FIGS. 12A-12D, the first crank shaft 12 is rotated around a center O (the first input/output shaft 4 a and the second input/output shaft 4 b), in the counterclockwise direction, by the rotation of the (the first input/output shaft 4 a and the second input/output shaft 4 b), by angles of 90°. By rotating the first crank shaft 12 around the center O (the first input/output shaft 4 a and the second input/output shaft 4 b) by the rotation of the input/output shaft, the second crank shaft 16 a is linearly reciprocally moved on a diameter R1 of a rolling circle 21 of a virtual circle 20, and the second crank shaft 16 b is linearly reciprocally moved on a diameter R2 of the rolling circle 21.

Namely, by rotating the first crank shaft 12 and the eccentric cam 13 (see FIG. 2), along a rotational orbit 22 having a radius of r and being centered around the axes of the first input/output shaft 4 a and the second input/output shaft 4 b (the center O), in the counterclockwise direction, the first piston set 14 of the piston sets linked with the eccentric cam 13, whose axes are the second crank shafts 16 a and 16 b, repeats the reciprocal movement on the diameter R1 of the rolling circle 21 (a concentric circle centered on the axis O) having a radius of 2 r, with relatively rotating to the cylindrical body 13 b, through the third bearing 19 a (see FIG. 2), and the second piston set 15 repeats the reciprocal movement on the diameter R2 of the rolling circle 21 having the radius of 2 r, with relatively rotating to the cylindrical body 13 b, through the third bearing 19 b (see FIG. 2). In the actual device, the eccentric cam 13 rotates relative to the first crank shaft 12 through the second bearings 18 a and 18 b, and the first piston set 14 and the second piston set 15 are reciprocally moved in the cylinders 5, which are perpendicularly arranged, with relatively rotating to the eccentric cam 13 through the third bearings 19 a and 19 b.

A rotational radius of the first crank arm, which connects the axis of the input/output shaft (the center O) to the first crank shaft 12, is set as r, and a length of the second crank arm, which connects the first crank shaft 12 to the second crank shafts 16 a and 16 b, is made equal to the rotational radius r of the cylindrical bodies 13 b, so that the eccentric cam 13 and the first and second piston units 14 and 15 (the piston unit P), which are assembled around the first crank shaft 12, can be compactly assembled in the axial direction and the radial direction (see FIG. 7).

In FIG. 2, a first piston head 14 b and a second piston head 15 b (see FIG. 8) are formed at both lengthwise ends of the first and second piston bodies 14 a and 15 a, Ring-shaped seal cups 14 c and 15 c (see FIG. 7) and seal cup holders 14 d and 15 d (see FIG. 7) are respectively fixed to the first piston head 14 b and the second piston head 15 b (see FIG. 8) by fixing screws 23. The seal cups 14 c and 15 c are composed of, for example, an oil-free sealing material (e.g., PEEK (polyether ether ketone) resin material).

In FIG. 2, the case body 3 (the first case member 1 and the second case member 2) has side surfaces (i.e., four surfaces), in which opening parts are respectively formed, and the cylinders 5 are respectively assembled therein. The first piston head 14 b and the second piston head 15 b (see FIG. 8) are capable of sliding on inner wall surfaces 5 a of the cylinders 5, and sealability therebetween is secured by the seal cups 14 c and 15 c (see FIG. 7). The outer peripheral edge of the seal cups 14 c and 15 c are bent along the inner peripheral surface of the cylinder 5. The seal cups 14 c and 15 c are assembled by overlapping seal cup holding plates 14 d and 15 d and screwing fixing screws 23 (see FIG. 7) with the first piston head 14 b and the second piston head 15 b (see FIG. 8).

In FIG. 3A, four screw holes 2 e for screwing fixing screws 3 a (see FIG. 11) are formed in each of corner parts 2 d of the second case member 2. In an inner bottom part 2 f of the second case member 2, four cylindrical bosses 2 g are provided on radially inside with respect to the screw holes 2 e. In FIG. 4, insertion holes 1 e, with which fixing screws 3 a (see FIG. 11) will be screwed, are formed in corner parts 1 d, which are located at one pair of diagonal positions in a top surface part of the first case member 1, and screw holes 1 g for fixing the attachment plate 9, described later, are formed in the corner parts 1 d, which are located at the other pair of diagonal positions (see FIG. 1). In FIG. 3B, four cylindrical bosses 1 i, which face the bosses 2 g of the second case member 2, are provided in an inner bottom part 1 h of the first case member 1 and located on radially inside with respect to the insertion holes 1 e and the screw holes 1 g. Shaft end parts of guide shafts 24, described later, are respectively fitted into boss holes 1 j and 2 h of the first case member 1 and the second case member 2, which are mutually faced, and held therein, then projected parts 24 a are fitted into the boss holes 1 j so as to prohibit rotation. A plurality of screw holes 1 k for fixing a first end surface cover 1 a (see FIG. 1) with fixing screws 1 b are formed on radially inside with respect to the bosses 1 i. Further, in FIG. 4, a plurality of fluid path holes 1 f are formed in the side surfaces of the first case member 1, and a plurality of fluid path holes 2 i are formed in the side surfaces of the second case member 2. (Note that, fluid paths communicated to a fluid inlet and a fluid outlet of the cylinder device may be optionally provided, so they are omitted in the drawings.)

In FIG. 6, the guide shafts 24, which are arranged in parallel to the input/output shaft (the first input/output shaft 4 and the first input/output shaft 5), are respectively fitted into the boss holes 2 h (see FIG. 4) of the bosses 2 g provided in the second case member 2. As shown in FIGS. 7 and 8, in each of the guide shafts 24, a first guide bearing 25, which receives lateral pressure of the first piston body 14 a, and a second guide bearing 26, which receives lateral pressure of the second piston body 15 a, are assembled coaxially and separated in the axial direction (see FIG. 8). Projected parts 24 a are radially outwardly projected from each of the guide shafts 24. The projected parts 24 a are fitted into the boss holes 1 j of the first case member 1 shown in FIG. 3B, so that they act as rotation stoppers. With this structure, rotation of the guide shafts 24 are prohibited by the case body 3, so that vibration of the guide shafts 24 is restrained, and abrasion between the guide shafts 24 and the case body 3 can be prevented. Note that, rotation of the guide shafts 24 may be prohibited by fitting them into the boss holes 2 h of the second case member 2 (see FIG. 4).

As shown in FIG. 3, the both shaft ends of each of the guide shafts 24 are held by corner parts where the first piston body 14 a and the second piston body 15 a are intersected in the case body 3, and each of the guide shafts is assembled in a state where the first guide bearing 25 abuts both side parts of the first piston body 14 a and the second guide bearing 26 abuts both side parts of the second piston body 26 (see FIG. 4).

With this structure, it is sufficient to provide required minimum number of the guide shafts 24 and the guide bearings 25 and 26 to the corner parts where the first piston body 14 a and the second piston body 15 a are intersected, so the device can be downsized. Further, the both end parts of each of the guide shafts 24 are held by the case body 3 (the first case member 1 and the second case member 2), so that vibration of the guide shafts 24 can be restrained, and durability of the device can be improved due to low vibration and low noise.

As described above, a plurality of the guide shafts 24 disposed parallel to the input/output shaft (the first input/output shaft 4 a and the second input/output shaft 4 b) are assembled in the case body 3 in the state where the first guide bearing 25, which receives lateral pressure of the first piston body 14 a, and the second guide bearing 26, which receives lateral pressure of the second piston body 15 a, are assembled coaxially and separated in the axial direction, so that the bearings for guiding the reciprocal movement of the first piston set 14 and the second piston set 15 can be consolidated, and an installation area can be minimized.

Concretely, an installation area of the case body 3 of the conventional device, which is shown in FIG. 13A and in which a pair of the guide shafts 24 and the guide bearings 25 and 26 are provided to the positions corresponding to the corner parts in the case body 3 where the first piston body 14 a and the second piston body 15 a are intersected with each other, the first guide bearing 25 for the first piston body 14 a is provided to one of the guide shafts 24 and the second guide bearing 26 for the second piston body 15 a is provided to one of the guide shafts 24, is defined as S1, and an installation area (an area shown by two-dot chain lines) of the case body 3 of the present embodiment is defined as S2; a ratio of S1/S2=1.45, so the installation area can be reduced by about 30% or more, and the device can be downsized.

Further, an installation area of the case body 3 of the conventional device, which is shown in FIG. 13B and in which the guide shafts 24 are penetrated though two long holes 14 f of the first piston body 14 a formed in a longwise direction, the first guide bearings 25 are respectively provided in the long holes 14 f, and the guide shafts 24 are penetrated though two long holes 15 f of the second piston body 15 a formed in a longwise direction, the second guide bearings 26 are respectively provided in the long holes 15 f, is defined as S1′, and the installation area (an area shown by the two-dot chain lines) of the case body 3 of the present embodiment is defined as S2; a ratio of S1′/S2=1.8, so the installation area can be reduced by about 45% or more, and the device can be downsized.

Therefore, in any cases, the lengths of the first and second piston bodies 14 a and 15 a can be shortened, so that the installation area can be reduced, it is sufficient to provide the four guide bearings 25 and 26 at the intersection part of the first piston body 14 a and the second piston body 15 a, number of parts can be reduced, and downsizing the device can be promoted.

An example of the structure of the rotary cylinder device is shown in FIG. 11.

Firstly, the piston unit P is assembled. the first piston set 14 and the second piston set 15 are assembled to the outer circumferences of the cylindrical bodies 13 b of the eccentric cam 13, through the third bearings 19 a and 19 b, in the state where the piston sets are intersected with each other, and the bearing holders 17 a and 17 b are assembled to the cylindrical hole 13 a together with the second bearings 18 a and 18 b. The first crank shaft 12 is fitted into the cylindrical hole 13 a of the eccentric cam 13, the first balance weight 11 a and the first input/output shaft 4 a are fitted to one shaft end part of the first crank shaft, and the second balance weight 11 b and the second input/output shaft 4 b are fitted to the other shaft end part thereof. Then, the pins 12 a and 12 c are penetrated through the first balance weight 11 a and the second balance weight 11 b and inserted into the shaft end parts of the first crank shaft 12 so as to correctly position. In this state, the pin 12 a and the fixing screw 12 b are perpendicularly screwed with the first balance weight 11 a, and the pin 12 c and the fixing screw 12 d are perpendicularly screwed with the second balance weight 11 b so as to integrally assemble.

In the second case member 2, the second end surface cover 2 a is previously fixed by the fixing screws 2 b, and the first bearing 2 c is assembled (see FIG. 2). The piston unit P is assembled by fitting the first input/output shaft 4 a into the first bearing 2 c held by the second case member 2. The guide shafts 24, on each of which the first and second guide bearings 25 and 26 are coaxially assembled and separated with a prescribed distance, are respectively fitted into the four bosses 2 g (see FIG. 4) formed in the inner bottom part 2 f of the second case member 2. With this structure, the first guide gearing 25 abuts the both side surfaces of the first piston body 14 a (see FIG. 10), and the second guide gearing 26 abuts the both side surfaces of the second piston body 15 a (see FIG. 9), so that they receive lateral pressures generated by the reciprocal movement of the first piston set 14 and the second piston set 15.

The cylinders 5 (see FIG. 5) are assembled in the four side surfaces of the second case member 2 with inserting the first piston heads 14 b and the second piston heads 15 b. The second input/output shaft 4 b is rotatably supported by overlapping the first case member 1 and sandwiching the cylinders 5. The case body 3 is integrally assembled by inserting the fixing screws 3 a into the insertion holes 1 e, which are formed in the top surface part of the first case member 1 and located at the diagonal positions, and screwing the same with the screw holes 2 e, which are formed in the second case member 2 and located at the corresponding diagonal positions.

In each of the cylinders 5, the cylinder heads 6 equipped with the sealing members 26 and the head covers 7 equipped with the sealing members 28 are overlapped and fixed to the side surfaces of the case body 3 by the fixing screws 7 a. Valve bodies 6 a, which is capable of switching inflow of a fluid from a fluid path to cylinder chambers and outflow thereof from the cylinder chambers to the fluid path, are provided to the cylinder heads 6.

The first end surface cover 1 a is overlapped onto the top surface part of the first case member 1 with the sealing member 8 and fixed by the fixing screws 1 b. The attachment plate 9 is fixed to the first case member 1 by inserting the fixing screws 10 into the insertion holes 9 a and screwed with the screw holes 1 g, which are formed at the diagonal positions in the first case member 1, so that the rotary cylinder device can be assembled.

In the assembled rotary cylinder device, a first static balance of the first and second piston sets 14 and 15 around the second crank shaft 16 a and 16 b, a second static balance of the piston unit P around the first crank shaft 12 and a third static balance of the first crank shaft 12 and the piston unit P around the input/output shaft are produced by the first and second balance weights 11 a and 11 b.

With this structure, when the first and second piston sets 14 and 15 assembled to the cylindrical body 13 are linearly reciprocally moved in the radial direction of the rolling circle 21 (see FIG. 12A) of the second crank shaft 16 a and 16 b, which is formed around the input/output shaft and has the radius of 2 r, by the rotation of the first crank shaft 12 around the input/output shaft and the relative rotation of the eccentric cam 13 around the first crank shaft 12, vibration caused by the rotation can be restrained, the device can be quiet, vibration caused by the rotation around the input/output shaft can be restrained, mechanical loss can be reduced, and energy conversion efficiency.

FIG. 14 shows graphs of examples of relationship between workload (input) of a compressor, whose discharge volume per rotation is 50 cc and whose pressure is 150 kPa, and the motor rotation speed. A graph A shows data of a compressor, which is driven by a reciprocal driving manner and in which static balance of an input/output shaft is produced by a conventional manner. A graph B shows data of a compressor driven by the rotary driving manner relating to the present embodiment. A graph C shows data of mechanical loss caused by reciprocal movement of a piston and a connecting rod, which are driven by the reciprocal driving manner.

According to the graphs, as shown by the graphs A and B, little difference is found between the graphs when the motor rotation speed is 1500 rpm or less; on the other hand, when the motor rotation speed is more than 3000 rpm, e.g., 3200 rpm, input of 267 W is required in the graph A, but input of 179 W is required in the graph B, so the input can be reduced by about 88 W (an arrowed part in FIG. 13). Therefore, by employing the rotary driving manner relating to the present embodiment, reducing energy consumption by about 33% can be realized.

Further, when rotating at high revolution number, e.g., more than 3000 rpm, mechanical loss is increased by the reciprocal driving manner as shown by the graph C, so it is understood that ineffectual workload is increased.

As described above, the lengths of the first and second piston bodies 14 a and 15 a in the lengthwise direction can be shortened, so the installation area can be highly reduced, and it is sufficient that only the four first and second guide bearings 25 and 26 are provided to the inter section part of the first piston body 14 a and the second piston body 15 a, so that number of parts can be reduced, and downsizing the device can be promoted.

Generating noise can be reduced (low noise) by reducing vibration caused by the rotation around the input/output shaft (low vibration), and generating heat and consuming electric power can be reduced by reducing mechanical loss. Especially, in case of rotating at high revolution number, e.g., more than 3000 rpm, electric consumption can be reduced by about 30% in comparison with that of the device driven by the conventional reciprocal driving manner.

Especially, a small and inexpensive motor, whose output power is about 30%, compared to the conventional reciprocal driving manner can be used as the driving source, so that reducing electric consumption can be promoted, a battery can be downsized, and an operable time of the device can be highly extended.

Therefore, downsizing and lightening device bodies of a compressor, a vacuum pump, a fluid rotary machinery, etc. can be promoted, so transportability of, for example, oxygen-condensing equipment can be highly improved. Further, if battery capacity is same, the operable time can be extended by about 30%.

Note that, clearances between the first and second piston bodies 14 a and 15 a and the first and second guide bearings 25 and 25, which receive their lateral pressures, are minimally designed, with considering machining errors and thermal expansion of structural parts so as to prevent mechanical interferences. 

1. A rotary cylinder device converting rotation of an input/output shaft, which is rotatably supported by a case body, into reciprocal movement of a plurality of piston sets, which are perpendicularly arranged with respect to an eccentric cam, according to the principle of hypocycloid, wherein a plurality of guide shafts, which are disposed parallel to the input/output shaft, are assembled in the case body, which accommodates a piston unit having first and second piston sets assembled to the eccentric cam and positioned in an axial direction, and wherein a first guide bearing, which abuts both side surfaces of a first piston body and receives only lateral pressure generated by the reciprocal movement, and a second guide bearing, which abuts both side surfaces of a second piston body and receives only lateral pressure generated by the reciprocal movement, are assembled coaxially and separated in the axial direction on each of the guide shafts.
 2. The rotary cylinder device according to claim 1, wherein each of the guide shafts has a projected part, which is radially outwardly projected, a shaft part thereof including the projected part is fitted into a shaft hole formed in the case body, and rotation of the shaft part is prohibited.
 3. The rotary cylinder device according to claim 1, wherein both shaft ends of each of the guide shafts are held by corner parts where the first piston body and the second piston body are intersected in the case body, and each of the guide shafts is assembled to a position at which the first guide bearing abuts both side surfaces of the first piston body and the second guide bearing abuts both side surfaces of the second piston body.
 4. The rotary cylinder device according to claim 2, wherein both shaft ends of each of the guide shafts are held by corner parts where the first piston body and the second piston body are intersected in the case body, and each of the guide shafts is assembled to a position at which the first guide bearing abuts both side surfaces of the first piston body and the second guide bearing abuts both side surfaces of the second piston body. 